A wire core barrel inner tube assembly releasably coupled to an overshot assembly for being moved through a drill stem.
In using prior art overshot and core barrel inner tube assemblies, (for example those disclosed in U.S. Pat. No. 3,120,283), if the coupled assemblies are sufficiently elevated by the wire line to completely clear the drill stem and then the inner (lower) end of the inner tube assembly moved away from the drill stem as the coupled assemblies are lowered for laying the assemblies flat on the earth surface, at times the conventional spearpoint will pivot in direction of the overshot dogs whereby the inner tube assembly becomes uncoupled from the overshot assembly and the outer end of the inner tube assembly falls. This can result in injury to the operator and damage to the inner tube assembly. Also in using the above procedure the overshot assembly of a type such as disclosed in U.S. Pat. No. 2,829,868 will bend at the jar staff, which at times results in damage to the overshot assembly.
A conventional procedure is to elevate the coupled overshot and inner tube assemblies sufficiently that the upper end portion of the inner tube assembly is above the drill stem, and then while still coupled, attach a pipe clamp to the upper end portion of the inner tube assembly. Thence a hook attached to the drill rig main hoist cable is hookingly engaged with a cable connected to the clamp and the hook elevated sufficiently that the overshot assembly can be and is uncoupled from the inner tube assembly. Thereafter the wire line hoist is operated to move the overshot assembly out of the way, and the main hoist to elevate the inner tube assembly to clear the drill stem, and while the lower end of the inner tube assembly is manually moved away from the drill stem, the hook is lowered so that the inner tube assembly can be laid flat on the surface. When an inner tube assembly is to be inserted into a drill stem, the pipe clamp is attached to the inner tube assembly, the main hoist operated to elevate the inner tube assembly and then lowered so that the inner tube assembly extends into the drill stem, the wire line hoist operated to move the overshot assembly to coouplingly engage the inner tube assembly, the pipe clamp removed and thence the wire line hoist operated to lower the coupled assemblies, provided the inner tube assembly is to be lowered by the use of the overshot assembly. This procedure can be dangerous, and does involve considerable handling of hooks, cables and etc. while switching from wire hoists to main hoists, which is time consuming.
In order to overcome problems such as the above, this invention has been made.